crash on character login

hello,
today i was about to test guild wars on the global free for all pvp event, but unfortunately some problems have occured. everything runs smothely, until i'm trying to login with my character. right after the game has completed loading, the game either crashes or the screen turns blue, saying something like that a critical error has occured, more than that you can't manage to read, as the computer reboots immediately.
In fact, ive already come across the same kind of problem. Sometimes when i'm closing ut2004, i see the same blue screen. It also happends when i'm trying to login to another mmorpg, rakion. However, multiple other games works just fine on my computer (ie EVE Online, World of Warcraft, FarCry...)

My hardware specifications:
AMD 64 3500+ (~2,2 ghz),
1024 mb DDR RAM,
GeForce 6800 GT (256 mb) (with latest drivers),
direct x9.0c

any ideas what could be the problem?